This invention relates to the pumps and compressors which incorporate adjustable inlet guide vanes for purpose of directing the fluid flow into the pump or the compressor rotating impeller.
Rotating fluid pumps and compressors are normally designed to operate best at specific fluid flow rate, pressure rise and rotating speed conditions. Process fluid flow systems often demand changes in the fluid flow rate, while maintaining relatively constant pressure rise. Such applications, very often employ pumps or compressors, operating at substantially constant rotating speed and include fluid flow control systems which bypass the excess fluid flow back to the pump or the compressor inlet by throttling of such fluid flow. Other control systems may utilize throttling of the entire pump flow, without the flow bypass. In such cases, a decrease in the fluid flow rate entering the pump or the compressor impeller causes a decrease in the axial fluid velocity while the rotational velocity of the impeller blades remain substantially constant. Such a condition causes higher relative inlet flow angle with respect to impeller blades, contributing to increase of blade inlet losses which negatively affect the pump efficiency and can produce unstable flow through the pump. Inlet guide vanes, producing pre rotation of the fluid flow in the direction of the impeller rotation, will decrease such high relative inlet flow angle, thus decreasing the blade inlet losses and increasing the impeller efficiency at such low flow conditions. Other applications, such as rotating air compressors used with turbochargers, boosting the pressure of internal combustion engines, are normally designed to achieve peak efficiency under pre-determined operating conditions. Change in the output power and rotating speed of internal combustion engine usually requires a cooresponding changes of charge air flow rate and the boost pressure delivered by the turbocharger to the engine. Such changes may result a decrease in the charge air flow rate, while the boost pressure demand remains disproportionally high. For instance, a reduction in the engine speed under high load conditions, usually decreases the ratio of the inlet air flow velocity relative to the rotatinal velocity of the turbocharger compressor blades, thereby producing higher inlet flow angle with respect to compressor impeller blades. Carefull matching of the turbocharger design to the specific engine requirements is needed, in order to avoid unstable compressor flows at such low flow conditions. Inlet guide vanes, causing pre-rotation of the air flow in the direction of the compressor rotation will, under such conditions, decrease the flow angle between the impeller blades and the air flow, thus allowing the turbocharger to achieve lower flow rates and increase its usefull flow range, while maintaining efficient compressor inlet flow conditions. Additionally, a fast responce of the inlet guide vanes system, when needed, during the engine and turbocharger acceleration, would be benefitial to the overall engine performance.
The use of inlet guide vanes in pumps and compressors to reduce the inlet flow angle for operating at conditions other than optimum is well known to the art. U.S. Pat No. 3,861,823 to George K. Serovy illustrates the use of inlet guide vanes,which are radially retractable in a linear fashion and which include automatic control system external to the fluid compressor. Such a control system, being connected to a system of ring gear, multiple pinion gears and rack members, inserts and retracts the guide vanes relative to the fluid flow.
Bladed turbine pump with adjustable guide vanes, in which the inlet guide vanes are linked to the second set of vanes located in the pump outlet, is described in the U.S. Pat. No. 4,484,857 to Pierre Patin. Such inlet guide vanes,being lengthwise pivotable, are continously submerged in the flow.
These approaches, while providing the desired inlet flow angle at part flow or at some other less than optimum conditions, use mechanical actuation systems, often employing ring gear, pinion gears, rack gears and levers. In order to maintain precise guide vanes alignment, such systems usually require a high degree of precision and minimum internal clearances between the mating parts, while at the same time allowing for manufacturing tolerances and thermal expansion differences that may occur in operation. Such mechanisms usually have relatively low tolerance toward particulate contamination between such mating parts. Repetitive cycling of such systems, with inlet guide vanes being subject to a great deal of turbulence generated by relatively high fluid velocities, tend to induce chatter and vibration into the guide vanes systems, which may lead to premature wear and malfunction of moving parts. Actuation systems, having multiple internal clearances in series, and which are required to transmit reversable motions, may also lag in responce when required to produce rapid and precise change of the inlet flow direction. Therefore, it would be desirable for such system to have a minimum mass inertia and no mechanical clearances between the individual parts.
It would be also desirable, for such guide vanes system, to be relatively insensitive to a particulate contamination in the fluid flow, with respect to its functional performance.